A Blog by Carl Zimmer

How Pigeons Cured My Case of YAGS

In tomorrow’s New York Times, I write about what pigeons taught Darwin about evolution, and what they can teach us over 150 years later. The spur for the story is a new paper in which scientists analyze the genomes of forty different pigeon breeds to understand the molecular secrets behind their remarkable diversity. My story is accompanied by some wonderful photos as well as a podcast in which I talk to my editor, David Corcoran, about the research.

Those who have ever been in earshot of me may find this story a bit puzzling. I have ranted many times about all the hoopla that bursts upon us every time the genome of yet another species is sequenced. Eventually my rants crystalized into a self-diagnosis: I realized that I suffered from YAGS, short for Yet-Another-Genome Syndrome. I first identified this disorder here on the Loom, and when I was asked to give a keynote talk at a genome science meeting last year, I explained it at more length. You can see the lecture in this video:

I got the sense from some of the scientists I talked to afterwards that my talk came off a bit nasty. That wasn’t my intention–I was just trying to convey just how exhausted I (and some other journalists I’ve spoken to) have gotten with the endless barrage of press releases that tout new papers on newly sequenced genomes.

It is unquestionably useful for scientists to do this work. The growing database of genomes has become a new territory for biological exploration. In some cases genomes turn out to be especially messy, and in these cases the scientists involved should be commended for their high pain threshold. Some genome studies even lead to fundamentally new methods of DNA sequencing, which is all for the good.

But the mere appearance of a new genome paper is not in itself reason for major news coverage. Nor are promissory notes for how valuable the genome sequences will be in the future. (Let’s wait till the future comes before we start reporting on it, shall we?)

Yet there is, in fact, lots of news about genomes worth reporting. Genome sequencing is getting so ubiquitous that scientists can fold it into their explorations of interesting questions about life. The mere existence of one pigeon genome won’t lead me to write a story. But a study that uses forty pigeon genomes to probe the evolution of new forms? Sign me up. The same goes for my recent Wired feature about using genome sequencing to track hospital outbreaks. The antidote to YAGS, in other words, is witnessing genomes in action.

One thought on “How Pigeons Cured My Case of YAGS

  1. You have left out one of Darwin’s most interesting finding on pigeons. In his 1842 essay, Darwin speculated that ancestral traits of vertebrates (gill clefts, notochord, etc.) have been retained in early embryonic development because of the mathematics of variation. He suggested that useful variations would in principle appear uniformly along development. Newly evolved structures would emerge gradually and cumulatively and leave the earliest embryonic features intact. As development advanced, ‘mutations’ would continuously kick in until finally the juvenile and adult stages were reached. To test his idea, Darwin, sometimes after 1855, compared metrics of hatchlings and adults of six fancy pigeon breeds to see how much adults differed in body proportions compared to hatchlings. If the body proportions of hatchlings were as different as those of adults, differentiation would have occurred entirely in the embryo. If hatchlings were similar and adults unlike, differentiation would be mostly post-hatching. Although Darwin did not explicitly state his expectation, his ‘constant variation hypothesis’ would suggest that much or most differentiation would have taken place prior to hatching, and nestlings and juveniles would display little more than finishing touches. However, Darwin found something very different. In five of the six breeds, hatchlings were very alike in body proportions compared to the adults of the same varieties. In short, most of the variation available to artificial selection, and by analogy to natural selection, was derived from genes expressed very late in development. The selective usefulness of variation appearing late in development helps clarify embryonic conservatism and, if you stop to think about it, why ‘weak recapitulation’ of the type championed by Ernst Haeckel might occur.

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